This invention relates to a recording and/or reproducing apparatus for an optical disc and an accessing method therefor. More particularly, it relates to a recording and/or reproducing apparatus for an optical disc employing lens shift signals, and an accessing method therefor.
Heretofore, an optical disc, such as a so-called CD (Compact Disc) or a MD (Mini-Disc), has been used as an optical recording medium for variable information signals, such as audio information.
A recording and/or reproducing apparatus for recording information signals on an optical disc or reproducing information signals recorded on the optical disc is configured for converging a light beam radiated from a laser light source provided on an optical pickup on a signal recording surface of the disc. The recording and/or reproducing apparatus generates tracking error signals, indicating the relative position of a track on the signal recording surface with respect to a light spot of a light beam, based on a light beam reflected from the signal recording surface of the disc, to perform tracking servo control for causing the light spot of the light beam to trace the tack optimally based on the tracking error signals.
To this end, the recording and/or reproducing apparatus includes an actuator and a sled mechanism for causing radial movement of the entire optical pickup along the radius of the disc. The actuator operates for converging the light beam from the laser light source with respect to the signal recording surface of the disc or causing the movement of an objective lens in the focussing direction, that is in a direction towards and away from the disc to permit the light spot of the laser light to optimally trace the track.
Meanwhile, among the recording and/or reproducing apparatus for recording information signals on an optical disc, such as a CD or an MD, or reproducing the information signals recorded on the optical disc, there is a portable type apparatus, in addition to a desk type apparatus. In the portable apparatus, the attitude of the apparatus itself is changed omnidirectionally under variable using conditions. Thus, in the portable recording and/or reproducing apparatus, the objective lens in an optical pickup is shifted from a mid-point position or neutral position, along the focussing direction and along the tracking direction, under the effect of the force of gravity, depending on the attitude of the apparatus.
Thus, in a conventional portable recording and/or reproducing apparatus, the block of the optical system needs to be designed so that, even if the objective lens is offset from the neutral position, recording and/or reproducing will be performed as normally. For example, if the position shifting of the objective lens along the tracking direction (radial direction of the disc) is taken into account, sufficient tolerance is afforded to the range of possible lens movement in the actuator adapted to drive the objective lens along the radius of the disc, in order that the optimum recording and/or reproducing operation will be initiated even if the objective lens is shifted from the mid-point position due to, for example, the force of gravity. The result is that the conventional recording and/or reproducing apparatus suffers from the problem that the structure of the optical block or the block of the electrical circuit controlling the optical block tends to be in size and/or in complexity.
Also, in the recording and/or reproducing apparatus for an MD, in which data is recorded on the disc in accordance with a photomagnetic system, a magnetic head needs to be mounted facing the laser illuminating position of the objective lens with the disc in-between. The result that, if the sufficient allowance is accorded to the range of lens movement along the radius of the disc, the structure of the magnetic head itself is also increased in size.
In view of the above problem, it is an object of the present invention to provide a disc drive device that is able to make recording and/or reproduction optimally under any attitude states.
It is another object of the present invention to reduce the size of e.g., an optical system in an optical pickup.
The present invention provides a recording and/or reproducing apparatus for an optical disc on which data have been recorded spirally or toroidally and address data are also recorded and which includes a pit area having the above data recorded as pits and a grooved area having a groove for recording the data. The apparatus includes an optical pickup, an error signal generating circuit, a shift signal generating unit and a servo controller. The optical pickup includes a light source for illuminating a light beam on the optical disc, an objective lens for converging a light beam radiated from the light source on the optical disc, a photodetector for receiving the light beam converged by the objective lens and reflected from the signal surface of the optical disc, and an actuator for moving the objective lens in a radial direction of the optical disc perpendicular to the optical axis of the objective lens. The photodetector has first to fourth photodetector segments split by boundary lines running parallel to the tracks of the optical disc. The error signal generating unit generates an error signal for moving the objective lens in the radial direction of the optical disc perpendicular to the optical axis of the optical disc, based on the amount of shift in the radial direction of the optical disc of the light beam converged by the objective lens on the signal surface of the optical disc to scan the track on the optical disc, based on output signals of the first to fourth photodetector segments. The shift signal generating unit generates a lens shift signal corresponding to the amount of shift from a neutral position of the objective lens, based on output signals of the first to fourth photodetector segments. The servo controller drives the actuator, based on at least one of the lens shift signal generated by the lens shift signal generating circuit and the error signal generated by the error signal generating unit, for moving the objective lens in the radial direction of the optical disc perpendicular to the optical axis of the objective lens.
The objective lens is set to a neutral position, by being moved based on the lens shift signal, and the tracking control can be made based on the error signal obtained based on the amount of deviation along the radial direction of the optical disc of the light beam from the neutral position, so that it is possible to realize the tracking control with stable high reliability.
The present invention also provides a recording and/or reproducing apparatus for an optical disc on which there are recorded data spirally or toroidally and on which there are also recorded address data. The apparatus includes an optical pickup, an error signal generating circuit, a shift signal generating unit and a servo controller, similar to those of the above-defined apparatus.
The present invention also provides a recording and/or reproducing apparatus for an optical disc on which data have been recorded by pits spirally or toroidally, and on which are also recorded address data. The apparatus includes an optical pickup, an error signal generating circuit, a shift signal generating unit, a servo unit and an optical pickup. The optical pickup includes alight source for illuminating a light beam on the optical disc, an objective lens for converging the light beam radiated from the light source on a signal surface of the optical disc, a photodetector for receiving the light beam reflected from a signal surface of the optical disc, a photodetector for receiving the light beam converged by the objective lens and reflected from the signal surface of the optical disc, and an actuator for moving the objective lens in a radial direction of the optical disc perpendicular to the optical axis of the objective lens. The photodetector has first to fourth photodetector segments split by boundary lines running parallel to the tracks of the optical disc. The error signal generating unit generates an error signal for moving the objective lens in the radial direction of the optical disc perpendicular to the optical axis of the optical disc, based on the amount of shift in the radial direction of the optical disc of the light beam converged by the objective lens on the signal surface of the optical disc to scan the track on the optical disc, based on output signals of the first to fourth photodetector segments. The shift signal generating unit generates a lens shift signal corresponding to the amount of shift from a neutral position of the objective lens, based on output signals of the first to fourth photodetector segments. The servo controller drives the actuator, based on at least one of the lens shift signal generated by the lens shift signal generating circuit and the error signal generated by the error signal generating unit, for moving the objective lens in the radial direction of the optical disc perpendicular to the optical axis of the objective lens. The controller controls the operation of the servo unit, while driving the movement mechanism based on the current position of the objective lens, the distance to the movement target position of the objective lens and on the lens shift signal outputted by the shift signal generating unit.
The controller finds the amount of the lens shift signal Ls based on the lens shift signal from the shift signal generating unit, and calculates the number of track jumps J based on the current position of the objective lens and the distance to the movement target position to the objective lens to calculate the amount of movement of the optical pickup by the movement mechanism based on the following relationship:
S=Ls+J.
The present invention provides an accessing method in a recording and/or reproducing apparatus for an optical disc on which there are recorded data spirally or toroidally and on which there are also recorded address data. The accessing method includes the steps of converging a light beam radiated from a light source by an objective lens on a signal surface of the optical disc, receiving the light beam converged by the objective lens and reflected from the signal surface of the optical disc by a photodetector having first to fourth photodetector segments split by boundary lines running parallel to the track of the optical disc, generating an error signal for moving the objective lens along the radial direction of the optical disc perpendicular to the optical axis of the objective lens based on an amount of shift along the radial direction of the optical disc of the light beam converged by the objective lens on the signal surface of the optical disc to scan the track of the optical disc, based on output signals of the first to fourth photodetector segments, generating a lens shift signal corresponding to the amount of shift from the neutral position of the objective lens based on the output signals of the first to fourth photodetector segments, and moving the objective lens along the radial direction of the optical disc perpendicular to the optical axis of the objective lens based on at least one of the lens shift signal and the error signals generated, while moving the optical pickup along the radial direction of the optical disc perpendicular to the optical axis of the objective lens, based on the current position of the objective lens, distance to the movement target position of the objective lens and on the lens shift signal, to control the position of the light beam relative to the track of the light beam.
Other objects and advantages of the present invention will become apparent from the following description which is made with reference to the accompanying drawings.